The Dijit Tree component lets you select multiple options by default and there is no easy way to turn that off, or atleast none that I could find. Ideally, this should be a configurable property, byt sadly, that’s not the case.
However, there is a “singular” property on the _dndSelector that would let us disable multi-select.

The easiest way is to just extend the Tree class and set singular: true :-